| 摘要 |
PROBLEM TO BE SOLVED: To reduce friction loss of a piston and a cylinder in all strokes, kinetic energy loss in an expansion stroke, and scuff of a piston skirt part against a cylinder wall. SOLUTION: A skirt part 3 is smoothly formed in such a way that a maximum diameter position A5 on more thrust side than a maximum diameter position B6 on the anti-thrust side is continuous above a piston axial direction L1 from maximum diameter curve faces A4 to A6 and B5 to B7 arranged above for the piston axial line L1 and each maximum diameter position A5, B6 on the thurst side and anti-thrust side and upper curved faces A1 to A3 and B1 to B4 in which a relief amount B0 in the direction of piston shrinkage diameter on the anti-thrust side is larger than a relief amount A0 in the direction of piston shrinkage diamter on the thrust side and lower curved faces A7 to A12 and B8 to B12 continuous below the piston axial line L1 from each maximum diameter position A5, B6 on the thrust side and the anti-thrust side are continuous in the direction of piston outer periphery.
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